PAEMELTA. 59 



Trees, and dead wood ; common ; and now (Illinois, Hall ; 

 Texas, Wright ; Mexico) scarcely differing from the European 

 lichen, but in smaller soredia. But our plant is mostly referable to- 

 ft, which occurs from Canada southward (Muhlenberg) Ach. Syn. 

 1814, to Louisiana (Hale] and Mexico. Earely (c) this blackens 

 beneath (South Carolina, Ravenel. Texas, Wright] and it passes, 

 finally, at the circumference, into narrower, sinuately lobulate 

 conditions suggestive as well of the two species next preceding, 



as of the closely akin following one. Though typically pale 



beneath, it is certainly the same plant which becomes finally, on 

 this side, blackish-brown. 



8.. P. saxatilis (L.) Fr. ; thallus narrowed, cartilagineous- 

 membranaceous ; soon more or less reticulately rimose, and lacu- 

 nose, often isidiophorous, glaucous-cinerascent ; beneath black, 

 and (now densely) black fibrillose ; lobes sinuately, often piu- 

 nately, many-cleft, retuse ; apothecia middling to large ; disk 

 chestnut, with an irregular, sub-crenulate margin. Spores 



ellipsoid, "^ mic. Fr. L. E. p. 61. Schcer. Spicil. p. 454. 



Nyl. Syn. 1, p. 388. 



b. sulcata, Nyl. ; lobes mostly wider and paler, besprinkled 

 with conspicuous, rounded or oblong, now confluent and reticu- 

 late soredia. Nyl. Licit. Scand. p. 99. P. saxatilis, v. rosce- 



formis, Ach., Tuckerm. Syn. Lich. N. Eng. p. 27. 



c. panniformis (Ach.) Schser. ; lobes short, densely crowded r 

 and imbricated. Ach. L. U. p. 469. Schcer. Spicil. p. 456. 



d. omphalodes, Fr. ; thallus brown, and blackening. Fr. 



I c. Nyl. I. c. 



Trees, dead wood, and rocks ; common in the northern States, 

 and northward (a, b) Muhlenberg Catal. 1818. Arctic America, 

 Richardson; Vahl. Wind River Mountains, Hayden. New 



Mexico, Fendler. West Coast, Lyall, etc. c, Arctic America, 



Herb. Hook. Vermont, /. L. Russell. White Mountains. d, 



rocks in mountainous and alpine districts ; White Mountains, 

 Oakes. British Columbia, Macoun. Arctic America. 



b. Stock of P. physodes. 



9. P. physodes (L.) Ach.; thallus rather loosely attached to 

 the substrate, more or less inflated, coriaceous-membranaceous, 

 glaucous-white; beneath brownish-black and black, smooth, 



